In most prior art methods of embossing designs, such as stitching, onto a thermoplastic sheet, both the anvil surface and the embossing die surface were rigid and relatively hard. In addition, the anvil surface was typically flat. The combination of the hard anvil surface and the hard embossing die surface provided an uneven distribution of pressure on the thin thermoplastic sheet as it was being formed; and this often produced undesirable distortions in the thickness of the sheet. In addition, to form raised bosses on the surface of the sheet, it was necessary to force the material to plastically flow from the high pressure debossing areas into the low pressure embossing regions. This required high temperatures, high pressures, and in general, dictated that the process be closely controlled because there was always the danger of projecting die features cutting through the thermoplastic sheet.
Some improvement in the embossed pattern is achieved by employing an unrestrained slab of elastomeric material as the embossing anvil. The elastomeric slab is intended to react to the pressure of the embossing die by undergoing a displacement such that the hot plastic sheet is more uniformly and completely forced into contact with the embossing die. However, I have found that unexpectedly a more sharply detailed pattern can be formed on a plastic sheet by employing as the embossing anvil an elastomeric section inlaid in a rigid supporting member.
Hereinafter, the term embossing is used to denote the overall process of imparting a design onto a formable sheet, wherein said design may have both raised and lowered features.